In this chapter, I describe the intended learning outcomes of scaffolding-content knowledge and higher-order thinking abilities-and link these to the goals advanced by the Next Generation Science Standards and related documents from recent curricular revisions in STEM education. Furthermore, I address different ways in which scaffolding's effect can be measured (assessment level), and explore whether there are differences in the magnitude of scaffolding's effect according to assessment level. Meta-analysis results show that there is no difference in effect size magnitude on the basis of intended learning outcome (i.e., content knowledge or higher-order thinking abilities). Scaffolding's effect was greater when measured at the principles level than when measured at the concept level. But scaffolding's effect was statistically greater than 0 and substantial for all three assessment levels (i.e., concept, principles, and application). These results are then discussed.